Hi MHF

I'm having some hard times with circular functions like

Let $\displaystyle A$ be a point on the curve $\displaystyle C: X^2+Y^2-2X -4=0$. If the tangent line to $\displaystyle C$ at $\displaystyle A$ passes through point $\displaystyle P(4,3)$, then the length of AP is:

It seems hard to even see the image in my mind, I'm confused!

Thanks in advance!